The opener smashed his third century of the tournament, the highest individual score in this year's tournament so far, to propel his team to an imposing 5-382.
Bangladesh never threatened to chase the target down. Having collapsed to 6-81 they eventually managed to reach 233 all out thanks to a battling run-a-ball 111 from Mahmudullah.
With the group stage now past the halfway mark - this was the 23rd match of 45 - India (10 points), New Zealand (8) and South Africa (8) have broken away.
Australia are in prime position to claim the fourth semi-final place. Like Pakistan and Afghanistan they have four points, but they have a game in hand, against Netherlands on Wednesday.
De Kock has announced he will quit one-day internationals after the World Cup and the left-hander appears determined to make his farewell a memorable one. he clobbered seven sixes and 15 fours.
"To be honest I am a bit more tired than satisfied," he said. "It was a great day out for the guys. Everyone did their part and it is nice to get another two points on the board."
South Africa had lost Reeza Hendricks and Rassie van der Dussen in successive overs after Aiden Markram, again leading the side in the absence of the unwell Temba Bavuma, won the toss and elected to bat.
De Kock combined with Markram (60) in a 131-run stand to steady the innings before he and Heinrich Klaasen tore apart the Bangladesh attack plundering 142 runs from 87 balls.
De Kock's exit brought no relief for Bangladesh as Klaasen and David Miller, who made 34 not out off 15 balls, continued the mayhem hitting a combined 12 sixes between them.
Klaasen belted 90 off 49 balls as South Africa plundered 144 runs from the last 10 overs.
"The top six/seven are different in their approach but it gels quite nicelysaid Markram.
After six quiet overs, Marco Jansen dented the Bangladesh top order removing Tanzid Hasan and Najmul Hossain Shanto with successive deliveries.
The match was effectively over when Bangladesh slumped to 4-42 inside 12 overs with skipper Shakib Al Hasan and veteran Mushfiqur Rahim also back in the pavilion.
Mahmudullah hit four sixes and 11 fours but could only delay Bangladesh's fourth defeat in five matches. The scale of the loss means they replace England on off the bottom of the ten-team stage on net-run-rate.
"I thought we bowled well for the first 25 overs," said Shakib. "Then they kicked on, we didn't have any answers."
